A wavelength division multiplexed-passive optical network (WDM-PON) provides a high speed broadband communication service by using an inherent wavelength assigned to each subscriber. Accordingly, each subscriber receives a signal having a different wavelength corresponding thereto, so that a security is enhanced and a separate communication service is provided to each subscriber, thereby enlarging a communication capacity.
Conventionally, a method has been proposed wherein a central office and a subscriber terminal have a respective light source including a distributed feedback-laser diode (DFB-LD) element, thereby realizing the WDM-PON.
However, such method has problems that the DFB-LD element is expensive and a temperature control technique is complicated.
Accordingly, a technique using a wavelength-locked optical signal has been widely used by injecting an incoherent light source into a Fabry-Perot Laser Diode (FP-LD) of a low price, thereby implementing a WDM optical signal. Further, in order to obtain much broader transmission bandwidth, a wavelength-fixed optical signal has been also used as the WDM optical signal, wherein the wavelength-fixed optical signal can be provided by applying an injection light source to a reflective semiconductor optical amplifier (RSOA) and modulating a current of the RSOA.
Hereinafter, a configuration of a conventional wavelength division multiplexed-passive optical network 100 will be described in reference to FIG. 1. FIG. 1 shows a schematic block diagram for showing a conventional bidirectional communication in an injection-locked wavelength division multiplexed-passive optical network.
The injection-locked wavelength division multiplexed-passive optical network 100 includes a central office 110, a subscriber terminal 130, a remote note 120 for connecting the central office 110 with each subscriber terminal 130 and an optical cable 140.
The central office 110 has an A band injection light source 111, a B band injection light source 112, a light source distributor 113, a first 1×N optical multiplexer/demultiplexer 114 and a multiplicity of transceivers 115.
The remote node 120 has a second 1×N optical multiplexer/demultiplexer 121 and the subscriber terminal 130 has a plurality of transceivers 131.
The A band injection light source 111 is provided as a light source for an A band optical signal serving as a downstream optical signal. As the A band injection light source 111, an incoherent light source may be mainly used. The A band injection light source 111 generates the A band injection optical signal, and then transmits it to the light source distributor 113.
The B band injection light source 112 is provided as a light source for B band optical signal serving as an upstream optical signal, and, like the A band injection light source 111, an incoherent light source may be mainly used as the B band injection light source 112. The B band injection light source 112 generates the B band injection optical signal, and then transmits it to the light source distributor 113.
The light source distributor 113 receives the A band injection optical signal from the A band injection light source 111 and transmits it to the first 1×N optical multiplexer/demultiplexer 114 of the central office 110. Further, the light source distributor 113 receives a wavelength-locked A band optical signal from the first 1×N optical multiplexer/demultiplexer 114 of the central office 110 and transmits it to the optical cable 140 connected to the remote node 120.
In addition, the light source distributor 113 receives the B band injection optical signal from the B band injection light source 112 and transmits it to the second 1×N optical multiplexer/demultiplexer 121 of the remote node 120 through the optical cable 140. Further, the light source distributor 113 receives a wavelength-locked B band optical signal from the second 1×N optical multiplexer/demultiplexer 121 of the remote node 120 and transmits it to the first 1×N optical multiplexer/demultiplexer 114 of the central office 110.
The first 1×N optical multiplexer/demultiplexer 114 separates the A band optical signal received from the light source distributor 113 according to the wavelength thereof, and then, injects it to each transmitter of the transceivers 115 of the central office 110. For example, as the first 1×N optical multiplexer/demultiplexer 114, an arrayed waveguide grating (AWG) may be used.
As the transmitter of the transceivers 115, the Fabry-Perot Laser Diode (FP-LD) may be used and the transmitter generates the downstream optical signal to be transmitted to each subscriber.
Specifically, if the A band injection optical signal separated based on the wavelength thereof is injected to each transmitter of the transceivers 115, wavelength elements having a wavelength different from that of the injected optical signal are suppressed and wavelength elements having a wavelength equal to that of the injected optical signal is locked, thereby outputting the wavelength-locked A band downstream optical signal.
Each receiver of the transceivers 115 receives a wavelength-locked B band upstream optical signal from the subscriber terminal 130, and then, converts it into an electrical signal. A photo diode (PD) may be used as the receiver of the transceivers 115.
The second 1×N optical multiplexer/demultiplexer 121 of the remote node 120 separates the B band optical signal received from the light source distributor 113 based on the wavelength thereof, and then, injects it to the transceivers 131 of the subscriber terminal 130. The arrayed waveguide grating (AWG) may be used as the second 1×N optical multiplexer/demultiplexer 121 like the first 1×N optical multiplexer/demultiplexer 114.
The Fabry-Perot Laser Diode (FP-LD) may be used as the transmitter of the transceivers 131, for example, and the transmitter generates an upstream optical signal to be transmitted to the central office 110.
Specifically, if the B band injection optical signal separated according to the wavelength thereof is injected to the transmitter of the transceivers 131, wavelength elements having a wavelength different from that of the injected optical signal are suppressed and wavelength elements having a wavelength equal to that of the injected optical signal is locked, thereby outputting the wavelength-locked B band upstream optical signal.
Each receiver of the transceivers 131 receives the wavelength-locked A band downstream optical signal from the central office 110, and then, converts it into an electrical signal. A photo diode (PD) may be used as the receiver of the transceivers 131.
Accordingly, as described above, the development of the light source distributor is strongly required, the light source capable of receiving the A band injection light source 111 as an input and outputting it to a common terminal of the first 1×N optical multiplexer/demultiplexer 114 of the central office 110 with a minimum optical loss; receiving the B band injection light source 112 as an input and outputting it to the optical cable 140 toward the remote node 120 with a minimum optical loss; transmitting the downstream optical signal outputted from the transmitter of the transceivers 115 of the central office 110 to the optical cable 140 with a minimum optical loss and transmitting the upstream optical signal outputted from the transceivers 131 of the subscriber terminal 130 to the common terminal of the first 1×N optical multiplexer/demultiplexer 114 of the central office 110 with a minimum optical loss.